The present invention relates to a cemented carbide and a coated cemented carbide member, and more particularly, to a cemented carbide for a coated cemented carbide cutting tool capable of imparting superior wear resistance and chipping resistance to a tool that machines various types of material to be machined, such as steel, cast iron, heat-resistant alloys and non-ferrous metals, and a coated cemented carbide member in which a hard coating layer is coated onto a surface of the cemented carbide.
In a coated cemented carbide cutting tool of the prior art, numerous proposals have been made to improve the opposite properties of wear resistance and chipping resistance while also improving cutting performance. One of these proposes a cemented carbide substrate having a surface region free of NaCl-type cubic crystal structure grains consisting of one or more types of a compound of a metal or metals of group 4, 5 or 6 of the periodic table, such as carbide, nitride or carbonitride (β-free layer) (J. of Japan Institute of Metals, Vol. 45 (1981), p.95). However, since a WC phase of the surface region of this cemented carbide substrate is consisting of coarse grains, resulting in large irregularities in the surface, and an amount of an iron family metal at the boundary between the surface region and the inner region decreases considerably, chipping resistance is not significantly improved while wear resistance is remarkably decreased.
On the other hand, Japanese Unexamined Patent Publication No. 2002-167640 discloses a coated cemented carbide member in which metal elements that form compounds of a metal or metals of group 4, 5 and 6 of the periodic table are nearly uniformly distributed in the surface region, although the metal elements excluding tungsten (W) are decreased in the surface region more than in the inner region of the substrate.
In addition, Japanese Unexamined Patent Publication No. 1995-180071 discloses a high-strength coated alloy comprising a cemented carbide substrate consisting of a three-layer structure. A first layer with a thickness of 0.5 to 5 μm comprises a WC phase, an NaCl-type cubic crystal structure phase consisting of carbide or carbonitride of a metal or metals of group 4, 5 or 6 of the periodic table and an iron family metal. A second layer with a thickness of 5 to 30 μm comprises the WC phase and a layer that is richer in the iron family metal than the inner substrate. A third layer with a thickness of 10 to 50 μm comprises the WC phase, the NaCl-type cubic crystal structure phase and a layer that is more deficient in the iron family metal than the inner substrate.
In the cemented carbide or the coated cemented carbide member, the NaCl-type cubic crystal structure phase having lower toughness than the WC phase is present in the surface region directly below the coating layer, resulting in improvement of wear resistance but decrease in chipping resistance.